1. Field of Invention
The invention relates to a method of seamless processing for merging 3D color images and, in particular, to a color processing method that achieves seamless effect using the brightness information and maintains the original colors without destroying its textures.
2. Related Art
When making three-dimensional (3D) images, seams are generated when combining two or more images due to the light source effect. This is particularly apparent for color images. Usually, we do not want to destroy the original textures and colors in the images. However, the different display coordinates make it very hard to use the usual planar image processing methods to solve the color difference problem occurring to the seams.
In order to achieve seamless image processing, many methods were proposed. For example, in “Correction for an Image Sequence” (Binh Pham, Glen Pringle, 1995 IEEE), some representative colors are selected in the overlapped area for obtaining a correction matrix to make the color consistent. Nevertheless, in addition to being only applicable to the overlap of two images, the method also has the following drawbacks:
(1) The selected representative colors will affect the correction result. The selection method cannot be widely applied.
(2) When the color difference between two regions is large, the effect will be worse.
(3) Since the colors of two regions are forced to be the same, the real color of the whole image is lost.
(4) Different reference colors have been chosen for different images. They cannot be applied to all images to effectively solve the discontinuity problem.
In “Computing Consistent Normals and Colors from Photometric Data” (H. Rushmeier and F. Bernardini), five light sources are put at different positions. The images are taken for an angle of an object using different light source individually. The five images are then synthesized into a single image with different weights, thereby solving the inhomogeneous problem caused by the light effect. The synthesized image is then merged with other similarly processed images. Thus the discontinuous phenomena around seams have diminished. Additionally, the neighborhood average method is used to solve the remaining discontinuity problem. The method is performed by directly averaging the color information RGB in the overlapped regions. Its shortcomings are:
(1) The seams processed using the proposed method still have lightly discontinuous phenomena.
(2) It is limited by the hardware setup and has a higher cost.
(3) While making a 3D display image, one has to repeatedly take images for five light sources individually for each angle of an object. It is thus very time-consuming.
(4) It still requires software corrections. Moreover, using the neighborhood average method to process the colors is likely to blur the image and loses the reality.
Besides the hardware solution, common technique such as linear or nonlinear weighted averaging performed by software is used to deal with seams at image boundaries. However, they all will blur the images at the edges and lose the detailed textures. Therefore, they are not ideal for the merges of several images or 3D images. The U.S. Pat. No. 6,271,847 warps the images and then blends the warped images using a weighted pyramid feathering scheme. The method works well and makes it possible to create seamless texture maps. However, it is likely to distort the color because it processes images within the RGB color space.